This invention relates to a stopper rod and particularly to a means of attaching a stopper rod to a lifting and lowering mechanism.
Stopper rods are well known for use in controlling molten metal flow from a vessel, e.g. a tundish, into a mould. A stopper rod is raised and lowered by a suitable mechanism positioned adjacent the vessel and can thereby be used to close fully or partially or open fully the outlet from the vessel, thus controlling flow of the metal from the vessel.
Conventionally, a stopper rod is formed as an elongate one-piece bonded graphite structure by isostatic pressing in a suitable mould. The stopper rod usually has a hollow structure in that it is formed to have a longitudinal, centrally-disposed bore by use of a suitable removable core in the mould. The lower end of the stopper rod bore may be closed or it may be vented to allow gas, e.g. argon, to be passed through the rod.
Thus, in the conventional manufacture of a stopper rod, the desired graphite composition is placed around a removable core in a deformable mould, i.e. the graphite composition fills the mould space between the core and the deformable mould. The deformable mould is then placed in a tank of liquid, for example water, and the pressure of the liquid is increased by known means to the pressure required to convert the graphite composition to the desired self-supporting structure. After removal of the isostatically pressed product from the mould, the core is removed to provide the hollow stopper rod.
The upper end of the rod must be provided with means by which it can be attached to the lifting and lowering mechanism. Various prior proposals have been made, including co-pressing a threaded bush in the upper end of the stopper rod to receive a threaded shaft; forming the upper end of the bore of the rod with an internal thread to receive an insert, e.g. of ceramic material, and placing a retaining pin through coterminous holes drilled through the stopper rod and an attachment rod.
While each prior proposal has certain merits, none is entirely successful and it is, therefore, an object of the present invention to provide an improved means of attaching a stopper rod to a lifting and lowering mechanism.
Accordingly, in one aspect the present invention provides a means of attaching a stopper rod in the form of an elongate moulded body having a longitudinal bore to a lifting and lowering mechanism, the means comprising a first sleeve to be moulded in-situ in the stopper rod body to lie coaxially with the stopper rod body in an annular recess surrounding and coterminous with the bore, the sleeve having a pair of circumferentially-spaced inwardly-directed, arcuate flanges, a connecting rod of diameter to fit into the stopper rod bore and of length to extend outside the stopper rod while passing through the first sleeve when the sleeve is in position in the stopper rod, the connecting rod having a pair of circumferentially-spaced, arcuate shoulders of size to pass through the spaces between the flanges of the first sleeve, whereby the connecting rod may be passed through the first sleeve until its shoulders have passed beyond the flanges of the first sleeve and then rotated until its shoulders are in circumferential correspondence with the flanges, and a second sleeve of external diameter to fit in the bore of the stopper rod and having at one end a pair of circumferentially-spaced, arcuate, axially-extending projections, the projections having an internal radius sufficient to accommodate the connecting rod through the second sleeve and the projections being of a size to fit into the spaces between the flanges of the first sleeve whereby the shoulders of the connecting rod may be locked beyond the flanges of the first sleeve.
In a second aspect, the invention provides a stopper rod fitted with the means of attachment to a lifting and lowering mechanism as defined in the immediately preceding paragraph.
The connecting rod is preferably externally-threaded, at least for a portion of its length intended to extend from the stopper rod, whereby it may be threadably connected to a corresponding portion of the lifting and lowering mechanism. (The lifting and lowering mechanism itself may otherwise be as conventionally used.) Alternative connecting means between the connecting rod and the lifting and lowering mechanism may, however, be utilised, if desired.
The bore of the stopper rod may extend for the entire length of the stopper rod or, if desired, the lower end of the stopper rod bore may be closed. In those embodiments where the lower end of the stopper rod is vented, i.e. the bore, albeit of possibly reduced diameter, extends throughout, so that gas, e.g. argon, may be passed through the stopper rod, the connecting rod should also have an axially-extending bore for that purpose.
The first sleeve, which may be of any suitable material, e.g. metal or ceramic material, is conveniently moulded into the desired position in the stopper rod body during the moulding of that body. Thus, for example, during the otherwise conventional isostatic pressing of the stopper rod in a mould containing a removable core to define the bore, the first sleeve is positioned in the desired position in the mould.
The first sleeve may be of circular outline in plan view but this is not essential. For example, it may be provided with one or more `flats`, i.e. flat-sided portions around its periphery in order to achieve better locking into position when it is moulded in-situ into the stopper rod body.
The second sleeve may also be of any suitable material, e.g. metal or ceramic material.
Preferably, the second sleeve is of such a height as to have its end remote from its projections lying in, or very close to, the plane of the upper end of the stopper rod when the attachment means is fitted. It is preferably of outside diameter such that it is a tight fit in the bore at the upper end of the stopper rod.
In a preferred embodiment, an apertured pressure disc is carried on the connecting rod and is maintained under pressure against the upper face of the stopper rod. It can thereby maintain pressure against the end of the second sleeve and thus ensure that, in use of the stopper rod, the second sleeve cannot move up the connecting rod and thereby loosen the locked nature of the attachment means. The pressure may be maintained by a nut threaded onto the connecting rod and rotated along the rod until it bears sufficiently on the disc.
If desired, of course, alternative means may be used to provide axially inward pressure on the end of the second sleeve to ensure that it remains in the locked position.
Sealing means may be provided as required. For example, a sealing washer may be positioned between the pressure disc and the upper face of the stopper rod and between the upper faces of the flanges of the first sleeve and the corresponding face of the second sleeve.